A known molten bath-based smelting process is generally referred to as the “HIsmelt” process and is described in a considerable number of patents and patent applications in the name of the applicant.
The HIsmelt process is applicable to smelting metalliferous material generally but is associated particularly with producing molten iron from iron ore or another iron-containing material.
In the context of producing molten iron, the HIsmelt process includes the steps of:
(a) forming a bath of molten iron and slag in a main chamber of a direct smelting vessel;
(b) injecting into the molten bath: (i) iron ore, typically in the form of fines; and (ii) a solid carbonaceous material, typically coal, which acts as a reductant of the iron ore feed material and a source of energy; and
(c) smelting iron ore to iron in the bath.
The term “smelting” is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce molten metal.
In the HIsmelt process solid feed materials in the form of metalliferous material (which may be pre-heated) and carbonaceous material are injected with a carrier gas into the molten bath through a number of water-cooled solids injection lances which are inclined to the vertical so as to extend downwardly and inwardly through the side wall of the main chamber of the smelting vessel and into a lower region of the vessel so as to deliver at least part of the solid feed materials into the metal layer in the bottom of the main chamber. The solid feed materials and the carrier gas penetrate the molten bath and cause molten metal and/or slag to be projected into a space above the surface of the bath and form a transition zone. A blast of oxygen-containing gas, typically oxygen-enriched air or pure oxygen, is injected into an upper region of the main chamber of the vessel through a downwardly extending lance to cause post-combustion of reaction gases released from the molten bath in the upper region of the vessel. In the transition zone there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
Typically, in the case of producing molten iron, when oxygen-enriched air is used, the oxygen-enriched air is generated in hot blast stoves and fed at a temperature of the order of 1200° C. into the upper region of the main chamber of the vessel. If technical-grade cold oxygen is used, the technical-grade cold oxygen is typically fed into the upper region of the main chamber at or close to ambient temperature.
Off-gases resulting from the post-combustion of reaction gases in the smelting vessel are taken away from the upper region of the smelting vessel through an off-gas duct.
The smelting vessel includes a main chamber for smelting metalliferous material and a forehearth connected to the main chamber via a forehearth connection that allows continuous metal product outflow from the vessel. The main chamber includes refractory-lined sections in a lower hearth and water-cooled panels in side walls and a roof of the main chamber. Water is circulated continuously through the panels in a continuous circuit. The forehearth operates as a molten metal-filled siphon seal, naturally “spilling” excess molten metal from the smelting vessel as it is produced. This allows the molten metal level in the main chamber of the smelting vessel to be known and controlled to within a small tolerance this is essential for plant safety. Molten metal level must (at all times) be kept at a safe distance below water-cooled elements such as solids injection lances extending into the main chamber, otherwise steam explosions become possible.
The HIsmelt process enables large quantities of molten iron, typically at least 0.5 Mt/a, to be produced by smelting in a single compact vessel.
One example of the construction of a solids injection lance for use in the smelting vessel can be found in U.S. Pat. No. 6,398,842 (assigned to the present applicant). This form of lance can be used to inject solid particulate material, such as metalliferous material or carbonaceous material, into the smelting vessel. Typically, the metalliferous material and carbonaceous material are injected through separate lances. The metalliferous material may be pre-heated. Metalliferous material and carbonaceous material may be co-injected through one lance.
The lance disclosed in U.S. Pat. No. 6,398,842 includes a central core tube and an outer annular cooling jacket. The core tube is fitted closely within the cooling jacket. In use, solid particulate material is passed through the central core tube and discharged from a forward tip end of the lance. A forced internal cooling water system is provided within the outer annular cooling jacket to allow the lance to operate successfully when exposed to the high temperatures encountered within a direct smelting vessel, which can be in excess of 1400° C. in the case of smelting iron ore as the metalliferous material.
Metalliferous material and carbonaceous material can be abrasive and therefore abrasive wear is a consideration in the design of a solids injection lance for the smelting vessel. This is particularly the case when the smelting vessel is used to produce molten iron and the metalliferous material comprises iron ore fines.
The use of an internal cooling water system in a solids injection lance, such as the lance disclosed in U.S. Pat. No. 6,398,842, is a safety issue that is a serious consideration in lance design. It is critical that solid feed material does not wear through the wall of the core tube of the lance and form a puncture and expose the water-cooling system to solid feed material, with a potential risk of an explosion.
A further consideration is that it is desirable that a direct smelting plant operate for a smelting campaign of 12 months or longer. It is therefore desirable to operate solids injection lances for as long as possible, taking into account safety considerations.
There are different types of solids injection lances for direct smelting vessels to the above-described water-cooled lance disclosed in U.S. Pat. No. 6,398,842. Other such lances include lances that separately inject solid feed material and an oxygen-containing gas into direct smelting vessels. These lances may or may not be water-cooled lances but are nevertheless subject to the same safety considerations arising from abrasive wear resulting in punctures of the solids injection components of the lances.
The present invention provides an effective and reliable solids injection lance for injecting metalliferous material and/or carbonaceous material into a direct smelting vessel.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.